Solder bonds are commonly used to attach modules such as multilayer ceramic packages to substrates such as printed circuit boards. For microelectronic applications, one technique of connecting an electronic component to a printed circuit board involves the use of multiple solder balls in an array. This technique, commonly referred to as ball grid array (BGA) technology, subsequently places the electronic package in registration with a printed circuit board and heats the assembly until the solder balls of the array flow to effect a connection to terminals on the printed circuit board or other substrate. With a BGA-type package structure, the solder balls function as external connection terminals on a connection surface.
One problem with this technology involves the fact that as the mulilayer package sizes are decreasing in all dimensions, the traditional solder interconnections are becoming a proportionately greater contributor to overall package height above the circuit board. As a greater amount of solder may result in a mechanically stronger bond which has greater reliability, it also has the adverse effect of adding to the overall height of the multilayer ceramic package.
Another problem with this technology is that the processes and steps required to properly position the various individual solder balls at exact predetermined positions on the underside of the multilayer package may be very elaborate. Oftentimes this is mechanically achieved by techniques such as a vacuum carrier or other robotic or precise placement equipment.
FIG. 1 and FIG. 2 show typical methods of using ball grid arrays in accordance with the prior art. Referring to FIG. 1, a semiconductor chip assembly 100 includes a semiconductor chip 1 joined to a chip carrier 2 by solder bumps 3 mated to pads 4. It should be noted that the semiconductor chip 1 rests a certain setoff distance "X" above the chip carrier 2.
Referring next to FIG. 2, a prior art BGA multilayer package 200 is provided with a group of bump terminals 1 which have been formed by joining solder balls 2 to the bottom surface of a multilayer ceramic package. Conductive paths 4 are formed within the mulltilayer package 200 itself. Once again, the solder balls 2 add significantly to the overall height of package 200.
FIG. 3 shows another embodiment of a semiconductor package 300 with a ball grid array in accordance with the prior art. In FIG. 3, a semiconductor element 1 is attached to a base 2. The element 1 is then wire bonded to the base 2 with wires 3 and the entire assembly is encapsulated in an epoxy or resin material 4. Significantly, an array of solder balls 5 form a grid on the underside of the base and provide a means for interconnecting the semiconductor element 1 with the external circuitry.
FIG. 4 shows still another example of a ball grid array in accordance with the prior art. In FIG. 4, a more elaborate semiconductor device 400 is provided. In this embodiment, the semiconductor element 1 rests upon a base 2 having conductive paths 3 therethrough. Solder balls 4 form a ball grid array which connect the element 1 with the external circuitry.
A mulilayer ceramic package with a ball grid array design which reduced the overall height of the ceramic package above a printed circuit board or other substrate, while simultaneously providing a high strength, reliable, interconnection of great integrity, and which is easily incorporated using conventional ceramic multilayer processing technologies and which reduced the number of processing steps and cost of equipment required to attach the multilayer ceramic package to the printed circuit board or other substrate would be considered an improvement in the art.